As gas sensors detecting gas, such as ammonia and nitrogen oxide, gas sensors that detect gas based on changes in electrical resistance have been conventionally used. The gas sensors detect the gas based on changes in electrical resistance of a semiconductor, such as tin dioxide, due to absorption of the gas on a surface of the semiconductor.
In the gas sensors that detect gas based on changes in electrical resistance, electric current needs to be supplied to the semiconductor using a constant-current power supply in order to measure changing electrical resistance. Therefore, the gas sensors that detect gas based on changes in electrical resistance have a problem that power consumption of a detection circuit itself becomes large.
Moreover, the semiconductor in the gas sensor needs to be heated to a temperature (for example, 400° C.) at which excellent detection properties can be obtained. Therefore, the gas sensor has a problem that a large quantity of power needs to be used for a heater configured to heat the gas sensor.
Accordingly, proposed are gas sensors, which detect gas based on changes in potential difference due to adsorption of the gas, not changes in electrical resistance. As such gas sensors, proposed are gas sensors using solid electrolytes having ion conductivity, such as oxygen ion conductivity, oxide ion conductivity, and proton conductivity (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 2002-031619, 2005-221428, 2007-248335, and 2009-198346).
In the proposed techniques, however, temperatures, at which the solid electrolytes for use (e.g., zirconia) exhibit excellent ion conductivity, are high temperature of 300° C. or higher. In the proposed techniques, moreover, a chemical reaction, such as an oxidation reaction, of gas to be adsorbed is used for causing a change in a potential difference in the solid electrolyte, and therefore the gas sensor needs to be heated to a temperature at which the chemical reaction is induced.
Accordingly, the proposed techniques have a problem that a large quantity of power needs to be used for a heater configured to heat the gas sensor.
Moreover, proposed as a gas sensor detecting gas at room temperature is a gas sensor, which is highly sensitive, is capable of highly selectively detecting NH3 gas at room temperature, and uses a CuBr film (for example, see Pascal Lauque, Marc Bendahan, Jean-Luc Seguin, Kieu An Ngo, Philippe Knauth, Analytica Chimica Acta, 515, (2004), 279-284). In the proposed technique, gas is detected based on a change in electrical resistance. Accordingly, it is necessary to supply electric current to the CuBr film using a constant-current power supply in order to measure changes in electrical resistance, and there is a problem that power consumption of a detection circuit itself becomes large.
Accordingly, there is currently a need for a gas sensor that does not require a supply of electric current using a constant-current power supply, does not need to be heated, and can be used with energy-saving efficiency, and a sensor device including such a gas sensor.